Finishing varnish for application over lithographic ink



Patented May 27, 1952 FINISHING VARNISH FOR APPLICATION OVER LITHOGRAPHIC INK Paul W. Greubel, Great Neck, N. Y., assignor to American Can Company, New York, N. Y., a corporation of New Jersey No Drawing. Application April 8, 1948, Serial No. 19,875

22 Claims. 1

The. present invention relates generally to finishing varnishes for lithographic inks and more particularly to novel improvements in those finishing varnishes which are applied over wet lithographic inks printed upon various web or sheet materials especially sheet metal, such as tin plate, terne plate, enameled sheet metal, etc. and to a method of varnishing over-wet lithographic ink, in which method the ink pigment is flocculated upon application of the varnish, and thereby preventing bleeding and ridging of the ink.

For many years it has been the practice, for example, in the decorated or lithographed sheet metal container art, to pass freshly lithographed metal sheets thru ovens for the purpose of drying the lithographic ink printed thereon before applying the finishing varnish which constitutes the final coating operation. Finishing varnishes are used to protect the lithographed surface and to improve its appearance by producing a hard, protective and glossy finish.

Later, attempts were made to economize these operations by applying the wet finishing varnish directly over the wet ink and then passing the Web or sheet thus coated thru the drying oven, thus drying both the wet ink and the wet varnish coats in a single operation. This process is known in the art as wet varnishing or wet ink varnishing. It saves considerable time and labor and would have many advantages if it were com-' pletely successful. However, the results obtained are unpredictable and have been far from satisfactorily uniform. It has been partially successful with only a relatively few finishing varnish formulations. In addition to restricting the use of many desirable and commercially required varnish formulations, the main difficulty has been inferior appearance such as lack of sharpness and lack of gloss in the finished lithographed product. More specifically, the inferior appearance is due to the bleeding or running'of the ink under the leveling action ofthe varnish coating, the ink flowing away from the printed areas at the edges; also the ink flows into macroscopic ridges or waves in the more solid areas thereby. producing a mottled and/or raised effect.

After extensive'observations, experiments and tests conducted over a considerable period of time, I discovered the causes or reasons for these undesirable results. ,I found that they ar'e'due to certain physico-chemical phenomena similar to those which occur in the processiof detergency. By experimenting with a great many different varnishes and inks, applying each varnish over a given ink and conversely applying a given varnish over each of a series of different inks and also mixing the respective inks and varnishes and observing them microscopically I found that in all cases of failures there occurred a local movement of the ink film similar in action to that of detergency or washing away and that the pigment particles of the ink film were always deflocculated. Close examination revealed that the two undesirable phenomena, i. e. bleeding or running and ridging or waving are the same in principle, each being the result of a disturbance or movement of the ink as levelling of the finishing varnish occurs. I also found that in all cases where bleeding and ridging did not occur, the pigment was always floc'culated and where these undesirable phenomena did occur the pigment was always in a state of deflocculation.

Upon discovering the reason or cause of the trouble, i. e. deflocculation of the ink pigment, I started the search for a proper remedy. It occurred to me that the difficulties couldprobably be overcome by searching out and utilizing lithographic inks and finishing varnishes which are completely or at least substantially immiscible. I soon discovered that this approach to the solution of the problem was impractical in view of the present state of the art. The film forming materials used in both inks and varnishes are usually essentially of the same general nature, i.e. both may be made from drying oils with or without resins or the finishing varnish usually contains a solvent which is also a solvent for the ink vehicle. Therefore, this method of approach would be successful only with very few and very carefully selected materials. This would severely limit the choice of materials from which the inks andfinishing varnishes could be made. Since commercial requirements make it imperative to have as wide a range of materials available as possible for use in this process, I searched for other means of solving the problem.

Next I thought --of producing a flocculated ink by incorporating a flocculating agent in the ink during its manufacture. This method also proved impractical because an ink strongly fiocculated before printing possesses certain undesirable characteristics which make it difficult to handle in the printing presses.

.ing varnish which on contact with the wet lithographic ink positively induces a strongly flocculated structure in the ink pigment and prevents bleeding or ridging of the ink when the varnish is applied over the wet ink.

Water and certain water soluble organic substances are known to induce flocculation in systems of solids in organic vehicles. Starting with this general knowledge I experimented with a great number of likely materials to test their suitability for my specific purpose. I discovered that while such flocculating materials come from various chemical classes or groups the suitable and successful ones, irrespective of their varying chemical composition, ultimately group them selves under a common class which can be defined by their common physical characteristics. They must all be liquids. They must all be substantially immiscible or at least of a very low order of miscibility with the ink vehicle-finishing varnish system. The term immiscible" is used in a relative sense. They must all be polar compounds.

Polar compounds are those in which the force uniting the atoms in the chemical bond is the electrostatic attraction between oppositely charged particles. This electrostatic attraction is present in ioniza-ble compounds and in compounds having electrostatic dissymmetry or ppositely charged groups in their spacial structure.

Immiscible liquids are those wherein one liquid will not blend or dissolve in another or will blend or dissolve only to a very limited degree, such that when they are poured together two distinct or separate layers or phases result. Absolute immiscibility may besaid to be non-existent and may be assumed to be useless as a flocculant I since this" would imply absolute immiscibility with the other liquids in the wet varnish system. Immiscible in connection with the present invention refers to a relatively low order of miscibility in the; ink'vehicle-finishing varnish system. The force of flocculation induced by immiscible liquids decreases as miscibility increases.

An'd finally these materials must be incorporated in the finishing varnish in certain percentages byweightwhich vary with different varnish compositions and ink-compositions, which percentages-will be effective in inducing immediate flocculation of the pigment in the lithographic ink.

While immiscibility or substantial immiscibility of the flocculating liquids is a necessary characteristic, I discovered that because of the low order of miscibility of these compounds this desirable characteristic is accompanied by the phenomenon of sometimes establishing a twophase system in the finishing varnish. Therefore it is sometimes necessary that the immiscible flocculant be rendered sufficiently accessible to the lithographic pigment, so that it can come into intimate contact with said pigment whereby it increases the'interfacial tension between the pigment surface and ink vehicle. which will result in immediate; strong flocculation of the lithographic ink pigment. I solved this problem by introducing a coupling agent or mutual solvent into the varnish composition. The coupling agent or mutual solvent must be miscible with the ink vehicle, the varnish vehicle and the flocculant. The function of the coupling agent or mutual solvent is to maintain the varnish flocculant mixture in a single continuous phase before application of the varnish to the inked surface and further to continue to maintain a single liquid phase when such mixture is applied to the wet ink so that the fiocculant can readily penetrate the ink vehicle layer to gain access to the ink pigment. Where a certain solvent already in the varnish composition is capable of functioning as a coupling agent, no additional or a lesser amount of coupling agent is required.

Among the flocculants which I have found to be satisfactory are:

(1) Water (2) Alkanols of from 1 to 3 carbon atoms inclusive suchas methanol, ethanol, isopropano'l, normal propanol (3') Lactic acid (commercial U. S. P. grade) (41) Formamide (5) Dihydrie alcohols of from 2 to 4 carbon atoms inclusive, such as: Ethylene glycol, proylene glycol, trimethylene glycol, diethylene glycol, etc.

(6) Glycerol For the purpose of the present invention I prefer to emphasize formamide.

All of the fiocculants. which I found. to be satisfactory, including those specifically mentioned. come under the definition relatively oil immiscible, water soluble polar liquids. The: Word oil in this definition for the purpose of my invention means-the water insoluble oil, resin or other filmforming materialsconstituting the. vehicle of lithographic inks.- My extensive ex.- periments and tests conclusively show that no material or compound which does/not come un der this definition functions as a satisfactory flocculant and conversely all materials. or compounds which do answer this definition are goodflocculants. Formami de falls. under the classification of relatively oil immiscible, water soluble polar liquids.

Formamidewith or without coupling agents isv incorporated into the finishing varnish. formulation, in such percentages by weight of complete The required percentage. of flocculant in: each commercial formulation of finishing varnish for stoppingv either. bleeding or ridging. can be readily and quickly determined by the iollowing: method:

Bleeding The method consists ofpreparing' several alfquotsof a given varnish, keeping one aliquot free of fiocculating agent as a control; and adding progressively increasing amounts of. floc'culatiii's'. agent or mixture of flocculants, and" couplingv agent where necessary; to the remainder;v A particular ink is rolled onto a; strip of white enameled metal plate, leaving a sharp, white uninked margin. One strip ofwet-inked plate is dipped (white margin down) into each-varnishflocculating agent mixture, and then allowed to drain. Bleeding, if present; will readily be observed against the background of the white: enamel.

Ridging To determine whether ridging is overcome,the preparation of finishing varnish-fiocculating agent aliquots, and rolling of a particular ink on a strip of white enameled metal plate is identical with the procedure described under bleeding. However, instead of dipping the strip of wetinked metal plate into the varnish, the varnish is applied over the wet ink by means of a roller. The plate remains flat at all times during this procedure. Ridging, if it occurs, can best be observed by looking at the ink from a 90 degree angle.

I have found that formamide is a very effective fiocculant in percentages of from about 2.5 to 13 per cent, but the practical range (which may be considered the critical range) is wider and extends from about 2 per cent to 15 per cent, depending upon the varying ifactors heretofore mentioned.

Where a coupling agent or mutual solvent is required, I found that the most satisfactory compounds are those which have a group that is water-like in character or which may be said to impart water soluble characteristics. The most desirable coupling agents all have a free organic hydroxyl or alcohol group or an acetylated alcohol group and all come under the classifications of aliphatic alcohols and glycol monoethers or acetates thereof. They may be graphically rep-- resented by R(O)R' in which R is an aliphatic carbon chain of 4 to 8 carbon atoms or a glycol monoether in which both the glycol and ether portions of the molecule extend from 2 to 4 carbon atoms and R is a hydrogen atom or an acetate radical.

The following are suitable as coupling agents either singly or in combination for all my purposes:

Examples of the film forming materials from which metal decorating finishing varnishes are generally prepared and with which the principles of the present invention may be successfully employed include:

A. Polyester polymers ALKYD RESINS Alkyd resins formed by the reaction of polyhydric alcohols and. polybasic carboxylic acids and their anhydrides, modified with non-drying, semi-drying or drying oils, with or without rosins, with or without mono or poly-functional phenolic bodies.

53.2% Soya modified alkyd resin solution 5.0%

solids (film former) 8.6% Formamide (flocculant) 38.2% Diethylene glycol monobutyl ether (coupling agent) POLYMERS F DIBASIC ACID ESTEBS OF UN SATURATED MONOHYDRIC ALCOHOLS 30.3% Diallyl phthalate (solid) (film former) 30.3% Acetic ester of diethylene glycol monobutyl ether (resin solvents) 15.1% Diacetone alcohol 9.1% Formamide (flocculant) 15.2% Diethylene glycol monobutyl ether (coupling agent) VINYL ESTER POLYMERS 22.0% Diethylene glycol monobutyl ether (coupling agent) C. Condensation polymers of aldehydes and amines or alcohols ALKYLATED REACTION PRODUCTS OF AMINES,

SUCH AS UREA OR MELAMINE AND AN ALDE- HYDE, SUCH AS EORMALDEHYDE 76.3% Urea-melamine aldehyde resin solution (50% solids) (film former) 6.1% Formamide (flocculant) 6.1% Butanol (coupling agent) 7 0.8% Liquid lubricant 10.7% Dimethyl phthalate (solvent for lubricant) 73.0% Urea-melamine aldehyde resin solution solids (film former) 11.7% Formamide (flocculant) 15.3% Diethylene glycol monobutyl ether (coupling agent) CONDENSATION POLYMER OF A POLYVINYL ALCO- HOL AND ALDEHYDE POLYVINYL BUTYRAL 6.6% Polyvinyl butyral (solid) (film former) 42.1% Butanol (resin solvent) 6.5% Formamide (flocculant) 0 44.8% Ethylene glycol monobutyl ether (coupling agent) D. Vinyl halide-vinyl ester copolymers VINYL CHLORIDE-VINYL ACETATE 12.4% Vinyl chloride-vinyl acetate (solid) (film former) I 21.7% Methyl isobutyl ketone 18.6% Xylene 9.3% Isophorone 1 10.0% Formamide (flocculan resin solvents pling agent) 28.0% Diethylenegly'col monobutyl ether (cou- E. Rosin-'- modified clear-estrous varnish 68.6 Rosin modified oleoresinou's varnish solution 70% solids (mm-romeo:

2.7% Formamide (fiocculautl 29.3% Diethylene glycol monobutyl: ether (cow pling agent) The formulae cited are typical examples of my invention and many more could be added.

A lubricant may be added to the finishing varnish if the sheet metal isto be subjected to fabricating processes after lithographing, The addition of the lubricant (which is optional) will of course vary the indicated percentages-of ingredients to a slight degree. Customarily, the -lubrlcant is added in the form of -a solution, and: the; amount added is regulated so that the lubricant sollds are equivalent to approximately 2 to 4 percent of the resin solids in the finishing varnish.

The inclusi'onor exclusionof a lubricating material has been found to be without effect on the pigment fiocculating ability of formamide.

The finishing varnish may be prepared without regard to whether the entire film former is manufactured in a snigl'ecperation, or'ifa hard" resin is first formed and then combined with a drying oil in a varnish kettle or if a solid resinis dissolved in solvents. Further, these groups of film formers may be used singly, or in any compatible combination, depending on the film characteristics desired. Anyone skilled in the art of varnish making will be able-to prepare the various varnishes which may be used in connection with my disclosed invention.

The above examples are for the purpose of i1- lustrating the essential spirit of the present-invention; that is to say, the finishing varnish is formulated in such a manner" as to: enable the same to induce a fiocculated structure in the lithographic ink.

My extensive experiments conclusively indicate that the finishing varnish as covered by the invention hereinbefore described may be applied over any and all wet lithographic inks composed of organic and/or inorganic pigments dispersed in a drying oil and/or resin-r modified drying oil and/or other ink vehicles such as-are ordinarily used. in lithography, especially metal-lithography.-

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it wi ll be apparent that various changes or modifications may be made in the compositions described without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the compositions hereinbefore describedbeina merely a preferred embodimentthereof.

I claim:

1. A finishing varnish for application over wet lithographic ink, said finishing varnish comprising in combination an alkyd resin as afilm forming material, 2 to by weight based on the finished varnish of a. pigment flocculatin'g agent consisting of formamide, and a volatile organic solvent for said resin and flocculating agent, said solvent being miscible with the ink. vehicle and containing sufficient coupling agent selected from the group consisting: of unsubstituted monohydricr alkanols having from 4 to 8 carbon atoms and glycol monoethers having from 2 to 4- carbon atoms in the glycol portion of the molecule and having one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms to maintainthe ingredients in a single liquid phase:

2'. A- finishing varnish for application over wet lithographic ink, 'said finishing varnish comprising in combination, an organic solvent soluble synthetic resin selected fromthe group consisting of alkyd-resins, polymerized d'ibasic acid esters of unsaturated-monohydric alcohols, organic acid polyvinyl esters; polyethers of polyhydroxycompounds, condensation polymers of amines and aldehydes, condensation polymers of aldehydes and: polyvinyl alcohol, and copolymers of vinyl halides and organic acid vinyl esters as film forming materials, 2 to 15% by weight based on the finished varnish of a pigment-fiocculating agent consisting of formamide, and a volatile organic solvent forsaid resin and saidfiocculating agent, said solvent being miscible with the inkvehicle and containing sufiicient coupling agent selected from the group consisting of unsubstituted monohydric alkanols-having from 4 to 8 carbon atoms and glycol monoethers having from 2 to 4 carbon atoms in the glycolportion of the molecule and having: one free hydroxylgroup and the other hydroxyl group etherified with an aliphatic hydrocarbon. substituent having. from: 2' to 4 carbon atoms, to maintain the ingredients in a single liquid phase;

3. A finishing varnish for application over wet lithographic ink, said finishing varnish comprising in combination, an organic solvent soluble synthetic resin selected from the group consisting of: alkyd resins, polymerized dibasic acid esters of unsaturated monohydric alcohols, organic acid polyvinyl esters, polyethers of poly-hydroxycompounds, condensation polymers of amines and aldehydes, condensation polymers of aldehydes and polyvinyl alcohol, and copolymers of vinyl halides and organic acid vinyl esters as film forming materials, 2 to 15% by weight based on the finished varnish of a pigment fiocculating agent consisting of formamide, and a volatile organic solvent for said resin and said'fio'cculating agent, said solvent being miscible with the ink vehicle and containing sufiicient unsubstituted monohydric alkanols having from 4 to 8 carbon atoms: as a coupling agent to maintain the ingredients in a single liquid phase.

4. A finishing varnish for applicationover wet lithographic ink, said finishingvarnishcomprising in combination, an organic solvent soluble synthetic resin selected from-the group consisting of alkyd resins, polymerized dibasic acid esters of unsaturated monohydri'calcohols,,organic acid polyvinyl esters, polyethers of polyhydroxy compounds, condensation polymers of amines and aldehydes, condensation polymers of aldehydes and polyvinyl alcohol, and copolymers of vinyl halides and organic acid vinyl esters as film forming materials, 2 to 15% byweight based on the finished varnish of an oil immiscible-water soluble polar'liquid consisting of formamide as a pigment fiocculating agent, andia volatile organic solvent for said resin and said fiocculating agent, said solvent being miscible'with the ink vehicle and containing sufficient glycol monoether having from 2 to 4 carbon atoms in the glycol portion of the molecule and having one free hydroxyl group and the other hydroxyl group etherified with a hydrocarbon substituent having from'2 to 4 carbon atoms, as a coupling agent to maintain the ingredients in a' single liquid phase.

a 5. A finishing varnish for application over wet lithographic ink, comprising in combination an organic solvent soluble synthetic resin as a film forming material, 2 to 15% by weight based on the finished varnish of formamide as a pigment fiocculating agent, and a volatile organic solvent for said resin and said fiocculating agent, said solvent being miscible with the ink vehicle and containing sufiicient unsubstituted monoalkanol having from 4 to 8 carbon atoms to maintain the ingredients in a single liquid phase.

6. A finishing varnish for application over wet lithographic ink comprising in combination an organic solvent soluble synthetic resin as a film forming material, 2 to 15% by weight based on the finished varnish of formamide as a pigment fiocculating agent, and a volatile organic solvent for said resin and said fiocculating agent, said solvent being miscible with the ink vehicle and containing sufiicient glycol monoether in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group,

the other hydroxyl group being etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms, as a coupling agent to maintain the ingredients in a single liquid phase.

'7. A finishing varnish for application over wet lithographic ink comprising in combination an organic solvent soluble synthetic resin as a film forming material, 2 to 15% by weight based on the finished varnish of a pigment fiocculating agent consisting of formamide, and a volatile organic solvent being miscible with the ink vehicle and for said resin and fiocculating agent, said solvent containing sufiicient coupling agent selected from the group consisting. of unsubstituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers having from 2 to 4 carbon atoms in the glycol portion of the molecule and having one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms to maintain the ingredients in a single liquid phase.

8. A method of wet ink varnishing comprising, printing a pigmented film forming lithographic ink on a sheet of web material and fiocculating the ink pigment by applying over the wet ink a finishing varnish containing an organic solvent soluble film forming resin in solution in a volatile organic solvent, 2 to 15% by weight based on the finished varnish of formamide as an oil immiscible-water soluble fiocculating agent for the lithographic ink pigment said solvent being miscible with the ink vehicle and containing sulficient coupling agent selected from the class consisting of unsubstituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

9. The method in claim 8 in which the resin is selected from the group consisting of alkyd resins, polymerized dibasic acid esters of unsaturated monohydric alcohols, organic acid polyvinyl esters, copolymers of vinyl halides and organic acid vinyl esters, condensation polymers of aldehydes and polyvinyl alcohol, condensation polymers of amines and aldehydes, and polyethers of polyhydroxy compounds.

10. The method of claim 9 in which the coupling agent is an unsubstituted monohydric alkanol having from 4 to 8 carbon atoms.

11. The method of claim 9 in which the cou- 10 pling agent is a glycol monoether having 2 to 4 carbon atoms in the glycolportion of the molecule and having one free hydroxyl group and the other etherified with an aliphatic hydrocarbon substituent having 2 to 4 carbon atoms.

12. The method of claim 8 in which the resin is a synthetic resin that is soluble in a volatile organic solvent.

13. The method of claim 12 in which the varnish resin isa volatile organic solvent soluble polymer formed by resinfying a compound having a vinyl group.

14. The method of claim 12 in which the resin is a condensation polymer of amines and aldehydes.

15. The method of claim 12 in which th varnish resin is an alkyd resin.

16. The method of claim 8 in which the web material is a metal sheet.

17. The method of claim 16 in which the metal sheet is tin plate.

18. The method of claim 16 in which the metal sheet is steel.

19. A finishing varnish for application over wet lithographic ink, said finishing varnish comprising in combination, an organic acid polyvinyl ester as a film forming resin, 2 to 15 per cent by weight based on the finished varnish of an ink pigment fiocculating agent consisting of formamide, and a volatile organic solvent for said resin and said fiocculating agent, said solvent being miscible with the ink vehicle and containing sufiicient coupling agent selected from the class consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers having from 2 to 4 carbon atoms in the glycol portion of the molecule and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

20. A finishing varnish for application over wet lithographic ink, said finishing varnish comprising in combination, a resinous polyether of polyhydroxy compounds as a film forming ingredient, 2 to 15 per cent by weight based on the finished varnish of an ink pigment fiocculating agent consisting of formamide, and a volatile organic solvent for said polyether and said fiocculating agent, said solvent being miscible with the ink vehicle and containing sufi'icient coupling agent selected from the class consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

21. A finishing varnish for application over wet lithographic ink, said finishing varnish comprising in combination a condensation polymer of an amine and an aldehyde as a film forming ingredient, 2 to 15 per cent by weight based on the finished varnish of an ink pigment fiocculating agent consisting of formamide and a volatile organic solvent for said polymer and said fiocculating agent, said solvent being miscible with the ink vehicle and containing suificient coupling agent selected from the class consisting of unsubstituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion-of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group 11 and the other hydroxyl group'etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms to maintain the ingredients in a single liquid phase.

22. A finishing varnish for application over wet lithographic ink, said finishing varnish comprising in combination a resinous copolymerof vinyl halide and an organic acid vinyl ester as a film forming ingredient, 2 to 15% by weight based on the finished varnish of a pigment flocculating agent consisting of formamide, and ;a volatile organic solvent for said copolymer and said flocculating agent, said solvent being miscible with the ink vehicle and containing sumcientcoupling agent selected from the class consisting of un substituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has .from 2 to 4 carbon atoms and one :free hydroxyl group and theother hydroxyl group etherified with an aliphatic hydrocarbon :chain having from 2 to 4 carbon atoms to maintain the ingredients in a single liquid phase.

PAUL W. GREUBEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,022,233 Ellis Nov. 26, 1935 2,423,812 Clipper July 15, 1947 2,448,358 'Dang-elmajer Aug. 31, 1948 

1. A FINISHING VARNISH FOR APPLICATION OVER WET LITHOGRAPHIC INK, SAID FINISHING VARNISH COMPRISING IN COMBINATION AN ALKYD RESIN AS A FILM FORMING MATERIAL, 2 TO 15% BY WEIGHT BASED ON THE FINISHED VARNISH OF A PIGMENT FLOCCULATING AGENT CONSISTING OF FORMAMIDE, AND A VOLATILE ORGANIC SOLVENT FOR SAID RESIN AND FLOCCULATING AGENT, SAID SOLVENT BEING MISCIBLE WITH THE INK VEHICLE AND CONTAINING SUFFICIENT COUPLING AGENT SELECTED FROM THE GROUP CONSISTING OF UNSUBSTITUTED MONOHYDRIC ALKANOLS HAVING FROM 4 TO 8 CARBON ATOMS AND GLYCOL MONETHERS HAVING FROM 2 TO 4 CARBON ATOMS IN THE GLYCOL PORTION OF THE MOLECULE AND HAVING ONE FREE HYDROXYL GROUP AND THE OTHER HYDROXYL GROUP ETHERIFIED WITH AN ALIPHATIC HYDROCARBON SUBSTITUENT HAVING FROM 2 TO 4 CARBON ATOMS TO MAINTAIN THE INGREDIENTS IN A SINGLE LIQUID PHASE. 